Alarm Stage - When a stressor occurs, the body responds in what has previously been described as the fight-or-flight response. I hardly eat at all which I get yelled at by family members for this. I am working on getting off the Lyrica , was mg daily , now 50 to daily. Nutr Health, ;9 4: Here is a depiction of the chemical reaction:
Urinary System Anatomy
Since Every Gram Counts , it will be important to use every trick in the book to try and miminize the mass cost of all this. So if the exploration ship Arrow-Back becomes marooned in the trackless wastes of unexplored space and is listed as having 20 person-weeks of life support, it makes it really easy for Mr. Selfish to do the arithmetic and figure that he will survive for twenty weeks instead of one if he murders the other 19 crew members.
More democratically, if the rescue ship will arrive in 8 days 1. The crew draws straws , and the unlucky two who get the short straws have the opportunity to heroically sacrifice themselves so that the rest of the crew may live.
Naturally the kind way to do the math is when initially planning the mission. Multiply the number of crew members by the duration of the mission in days to get the required number of person-days of consumables and if you are wise you'll add an additional safety margin. Then you can calculate the mass and volume for each vital life-support consumable.
For instance, a day mission with 5 crew would need 1, person-days. If food takes up 2. A useful document with nitty-gritty details about life support Human Integration Design Handbook. This include info on the minimum volume needed for such tasks as exercise and hygiene, range of safe breathing mixes, temperature, humidity, acceleration limits, fire extinguishers, and related matter. The first three requirements are called "consumables", since they are gradually used up by the crew.
Each of those three can be controlled by either an "open" system or a "closed" system. Open systems are ones where a supply of the consumable in question is lugged along as cargo, enough to last the for the planned duration of the mission. It is renewed by "resupply", by obtaining new supply from a resupply spacecraft, a base, or an orbital supply depot.
Things can get ugly if the mission duration becomes unexpectedly prolonged, for instance by a meteor scragging the spacecraft's engine. Closed systems are ones where the supply of the consumable in question are renewed by some kind of closed ecological life support system.
Generally this takes the form of some sort of plants, who use sunlight to turn astronaut sewage and exhaled carbon dioxide into food plants and oxygen. Note that requirements for consumables can be drastically reduced if some of the crew is placed into suspended animation. If you want more data on life support than you know what to do with, try reading this NASA document. As a very rough rule of thumb: Of course this can be reduced a bit with hydroponics and a closed ecological system.
This also makes an attractive option out of freezing one's passengers in cryogenic suspended animation. Eric Rozier has an on-line calculator that will assist with calculating consumables. Many of the settlers of Talentar, who would later become dirt farmers and ecopoetic line techs, were drawn from rural areas of Eliéra, seeing an opportunity to apply their sophisticated knowledge of modern agriculture and silviculture to the problems of making this new world blossom.
It is from these settlers that a local variation in the rights and customs of hospitality has become ubiquitous. Many of the foresters and line techs of the Delzhía Terra region in particular were drawn from the wooded upland valleys of the Vintiver region. A traveler by foot or rover can stop at any of the small domes or prefabs dotting the dusty plains, signal at the service hatch, and receive a charge for their powercells, a fresh oxygen tank for an expended one, and a packed handmeal of the local produce — an invaluable service for traveling light, or in a pinch.
According to NASA, each astronaut consumes approximately 0. They breath out 0. At that pressure, one person day of oxygen takes up about 0. Stored as liquid oxygen, 0. This requires extra mass for the cryogenic equipment to keep the oxygen liquid, but the volume savings are impressive.
So as far as pure oxygen goes, you take 0. Repeat with the volume figure for the total oxygen volume requirement. However, this is just pure oxygen.
This is insanely dangerous to use as the ship's atmosphere, the accident that killed the Apollo 1 crew proved that. In practice one uses a "breathing mix" of oxygen and another gas. Generally the other gas is nitrogen. The technical term is " nitrox ". The shuttle space suits use 4. Setting up the optimal breathable atmosphere is complicated.
The amount of oxygen must be kept under strict limits or oxygen toxicity will harm the crew. The Bono Mars Glider uses a heliox atmosphere, but I cannot figure out why. For example, to avoid nitrogen narcosis, station air supplies are mixtures of oxygen and helium rather than oxygen and nitrogen.
This means that regular station residents speak with the squeaky cartoonlike voices that result when human larynxes vibrate in a helium environment. Those who live in such stations say they quickly become accustomed to the phenomenon. Psychological tests prove otherwise. Extended exposure to high-pitched helium voices causes severe subconscious stress, leading to a variety of mental disorders—from general anxiety and mood swings to clinical depression and outbursts of rage.
The reason is simple: Homo sapiens evolved as social animals, and they have a deep-seated need to hear voices that are recognizably human. These people are not researchers: Wherever these people go, they ease tension and make it possible for others to concentrate on their work. There are two methods of cracking CO 2 into C and O 2: Low energy requires huge amounts of biomass in plants.
Data from Biosphere II indicate roughly seven tons of plant life per person per day, with a need for roughly 4 days for a complete plant aspiration cycle, so call it 25 to 30 tons of plant per crewman. With an average density of 0. High energy methods take up much less space, but as the name implies requires inconveniently large amounts of energy.
It also results in lots of messy by-products and waste heat. Practically, it is easier to flush the CO 2 instead of cracking it, and instead bringing along an extra supply of water to crack for oxygen. Water is universally useful with a multitude of handy applications, and takes less energy to crack than CO 2.
For future Mars missions, it has been suggested that the life support system should utilize the Sabatier Reaction. This takes in CO 2 and hydrogen, and produces water and methane. The water can split by electrolysis into oxygen and hydrogen, with the oxygen used for breathing and the hydrogen used for another batch of CO 2.
Unfortunately the methane accumulates, and its production eventually uses up all the hydrogen. For emergency use, it would be wise to pack away a few Oxygen Candles.
These are composed of a compound of sodium chlorate and iron. Molecular Product's Chlorate Candle 33 masses It is not enough to supply oxygen to breath, you also have to remove the carbon dixoide. Bad things happen if the CO 2 levels rise too high. NASA says that each astronaut exhales 0. In the Apollo program spacecraft, NASA used lithium hydroxide based scrubbers, which fill up and have to be replaced.
Oxygen tanks have enough to last for the duration of the mission, and is gradually used up. Actually it is converted into carbon dioxide and is absorbed into the scrubbers, where it cannot be used any more. You may remember all the excitement during the Apollo 13 disaster, when NASA learned the life-threatening dangers of non-standardization. The crew had to use the Command Modules' scrubber cartridges to replace the ones in the Lunar module.
They had to rig an adaptor out of duct tape and whatever else was on-board. Metal-oxide scrubbers remove the CO 2 as before.
But when they get full, instead of being replaced, they can have the CO 2 flushed out by running hot air through it for ten hours. Then they can be reused. In the following specifications, the mass kg , volume m 3 , and electrical power requirements W is for equipment sized to handle a six person crew.
First the stale air is pumped through a 4-Bed Molecular Sieve It initially removes the water from the air and sends it to be added to the life support water supply , then it removes the carbon dioxide.
The carbon dioxide and some hydrogen from a source to be explained shortly are fed into a Sabatier Reactor 26 kg, 0. They react producing methane and water: The methane is vented into space. The water is fed into an electrolyser to be split into hydrogen and oxygen. The hydrogen is sent back to the Sabatier Reactor to take care of the next batch of carbon dioxide.
The oxygen is added to the breathing mix and released into the habitat module's atmosphere. The TransHab starts out with a tank of high pressure oxygen The oxygen tank has three days worth of breathing for six crew, enough to give the Sabatier Reactor time to get started.
The nitrogen tank has enough to establish the proper ratio for the breathing mix, and some extra to compensate for any atmosphere leaking into space.
Jensen; someday you'll come a cropper with a planet that is new to you! As I was saying, we got this rust infection about ten days out. I didn't have any more farm than an Eskimo. I cleaned the place out, sterilized, and reseeded. The infection was all through the ship and I couldn't chase it down.
We finished that trip on preserved foods and short rations and I wasn't allowed to eat at the table the rest of the trip. I exhausted the air from an empty compartment, suited up, and drilled a couple of holes to the outside.
Then I did a piping job to carry foul air out of the dark side of the ship in a fractional still arrangement — freeze out the water first, then freeze out the carbon dioxide. Pesky thing was always freezing up solid and forcing me to tinker with it. But it worked well enough to get us home. Bart and Dan went off to do that, and Jim followed behind them. But from their faces, he could tell that their hopes weren't too high.
Obviously, most of the oxygen had been put into the new extension, since there was more room there for the big containers of liquid oxygen. They had been in the shadow, below the main part of the hull, where they could stay liquid; but the heat of the fire had bent and twisted them, and some had even exploded violently.
Gauge will tell you what per cent has been used. It was a lot less than they would have liked. And we don't have chemicals to soak up the carbon dioxide they breathe out for even that long. In a vague way, Jim still felt responsible for the trouble. He should have checked on his assistant. He'd been beating his head, trying to remember what he'd learned in high school about the behavior of the gas. His father had always maintained that a man could accomplish almost anything by reducing things down to the basic characteristics, and then finding out what was done in other fields.
He realized his mistake before the others swung on him. What are the basic characteristics of carbon dioxide? The young man who'd studied chemistry piped up again. Animals breathe it out, and plants breathe it in, releasing the oxygen again.
It freezes directly to a solid, without any real liquid state, and is then known as dry ice. What about the cold side—does it get cold enough to freeze it out? Dan, any way to get a gastight pan. We could blow it through there slowly enough—trial and error should tell us how slowly. In most space program, they use two breathing mixes for the atmosphere inside the habitat modules and space suits.
Low Pressure pure oxygen at High pressure breathing mix is pretty close to ordinary Terran air at sea level. The important thing to note is that for a low pressure breathing mix, the crew will die of anoxia if the atmospheric pressure falls below 5.
For a high pressure breathing mix, anoxia lies below The basic limit is anoxia ocurrs when the Partial Pressure of oxygen drops below 5. Anoxia will hit the crew when the atmospheric pressure drops to what pressure? Low pressure is attractive; since it uses less mass and the atmosphere will escape more slowly through a meteor hole. Unfortunately the required higher oxygen level make living in such an environment as hazardous as chain-smoking inside a napalm factory. NASA found that out the hard way in the Apollo 1 tragedy.
Since then NASA always uses high pressure, they use low pressure in space suits only because they cannot avoid it. This does raise a new problem.
There is a chance that the high-oxygen atmosphere will allow a meteor to ignite a fire inside the suit. There isn't a lot of research on this, but NASA seems to think that the main hazard is a fire enlarging the diameter of the breach, not an astronaut-shaped ball of flame. There are other problems as well, the impossibility of air-cooling electronic components and the risk of long-term health problems being two. A more annoying than serious problem with low pressure atmospheres is the fact that they preclude hot beverages and soups.
It is impossible to heat water to a temperature higher than the local boiling point. And the lower the pressure, the lower the boiling point. You may have seen references to this in the directions on certain packaged foods, the "high altitude" directions. The temperature can be increased if one uses a pressure cooker, but safety inspectors might ask if it is worth having a potentially explosive device onboard a spacecraft just so you can have hot coffee.
Decompression sickness also known as DCS, divers' disease, the bends or caisson disease is one of the more hideous dangers of living in space. It occurs when a person has been breathing an atmosphere containing inert gases generally nitrogen or helium and they move into an environment with lower pressure. This is commonly when they put on a soft space suit or the room suffers an explosive decompression. It has all sorts of nasty effects, ranging from joint pain and rashes to paralysis and death.
The large joints can suffer deep pain from mild to excruciating. The brain can have sudden mood or behavior changes, confusion, memory loss, hallucinations, seizures, and unconsciousness. The legs can become paralyzed. Headache, fatigue, malaise, loss of balance, vertigo, dizziness, nausea, vomiting, hearing loss, shortness of breath, and urinary or fecal incontinence: Why does it happen?
Well, imagine a can of your favorite carbonated soda beverage. Shake it up, and nothing happens. But when you open it, the soda explodes into foam and sprays everywhere. When you open the container of shaken soda, you lower the pressure on the soda fluid.
This allows all the dissolved carbon dioxide in the soda to un-dissolve, creating zillions of carbon dioxide bubbles, forming a foam. Now imagine that the carbon dioxide is nitrogen, the drink is the poor astronaut's blood in their circulatory system, and the foam is the deadly arterial gas embolisms.
That's what causes the bends. Please note that sometimes the bends can occur if one moves from one habitat to another that has the same pressure, but a different ratio of breathing mix the technical term is "Isobaric counterdiffusion".
Spacecraft of different nations or models could use different breathing mixes, beware. In fact, rival astromilitaries might deliberately utilize odd-ball breathing mixes, to make life difficult for enemy boarding parties invading their ships. The bends can be prevented by slow decompression , and by prebreathing. Or by breathing an atmosphere containing no inert gases.
Slow decompression works great for deep-sea divers but NASA does not favor it for space flight. An atmosphere with no inert gases pure oxygen is an insane fire risk.
NASA does not allow a pure oxygen atmosphere in spacecraft and space stations, but will allow it in space suit in a desperate attempt to lower the suit pressure to the point where the astronaut can move their limbs instead of being trapped into a posture like a star-fish. So NASA astronauts do a lot of prebreathing. This flushes nitrogen out of the blood stream. NASA uses Terra-normal pressure The astronaut s enter the airlock, and the airlock pressure is reduced to They breath pure oxygen through masks for 60 minutes because the air in the airlock contains nitrogen.
They then put on their space suits and do an EMU purge i. The air inside their suits is now also pure oxygen. The airlock pressure is then brought back up to the normal They then do minutes of in-suit prebreath. Of those minutes, 50 of them are light-exercise minutes and 50 of them are resting minutes. Thus "Slow Motion Hokey Pokey".
Now they are ready to open the airlock and step into space. The innovation was the 50 minutes of exercise. Without it, the entire protocol takes twelve hours instead of one hour and fifty minutes. If the habitat module's pressure was 12 psi an astronaut could use an 8 psi space suit with no prebreathing required a pity such suits are currently beyond the state of the art , and for a 4.
In case of emergency, when there is no time for prebreathing, NASA helpfully directs the astronauts to gulp aspirin, so they can work in spite of the agonizing pain. Please note that most of the problem is due to the fact that soft space suits have a lower atmospheric pressure than the habitat module. So this can be avoided by using a hard space suit or space pod. All of the atmospheric controls will be on the life support deck.
On a related note, forced ventilation in the spacecraft's lifesystem is not optional. In free fall, the warm exhaled carbon dioxide will not rise away from your face. It will just collect in a cloud around your head until you pass out or suffocate. In the image above the blue dome shaped flame is an actual candle burning in free fall. And in Clarke's "Feathered Friend", he talks about the wisdom of using an animal sentinel to monitor atmospheric quality.
Specifically by using the tried and true "canary in a coal mine" technique. I know most people like to tie little prayer flags and scarves and stuff to the air-vent to make sure it's working, but back home we use wind chimes.
You don't have to be looking at 'em to know they're working. They're not like the chimes they have back on Earth; these only have one note. Most habs around Saturn do it that way — each compartment has a single note. That way, you can tell location of a faulty blower just by the change in the sound. And let me tell you, they are not optional.
If you take a set down for anything other than maintenance on the air-vent in question, you can get arrested. Of course they're loud! That's how you know they're working. But I know what you mean — when I first moved out to Titan, it took me a good month to get used to 'em.
I was up all night most nights hearing chimes all over the hab ringing. It was like this constant drone with a few off notes every now and then to make sure you didn't relax. I complained to anybody who'd listen, which was nobody.
All I did was get myself a rep as another dumb groundhog fresh off the boat. The chimes didn't just bother me at night, either. In public spaces they make quiet conversation just about impossible. And I just about failed my first semester in school from being distracted. Seriously, if I hadn't still been under Immigrant's Probation, I would have had to do a public service sentence.
As it was, I did have to take the Habitat Orientation class again — listening to the damned wind chimes the whole time. But let me tell you — They were absolutely right to bust me. They confiscated my ear buds when I got caught so I didn't have them during a weekend maintenance cycle on the hab. We were living in a retired Trans-Chronian, the kind they used to have before the River -class came out.
The counter-spinning rings were always breaking down or getting fatigued or some damn thing, so we only had gravity maybe five days a week. My little sisters loved it — I'd play catch with them, with the toddler standing in as the ball. Anyway, the apartment had only pair of rooms, and my parents got one and the girls the other.
I slept in a bag in the living room and lived out of a foot locker. One night I woke up from a dead sleep with the uncontrollable feeling that something was wrong. I couldn't put my finger out what it was, but the effect was disturbing. I figured that I was just having trouble sleeping from the wind chimes when I realized that was what was wrong — I wasn't hearing the chimes.
A glance up told me that the chimes in the living room were still going, but I really didn't need it. The sound of all the chimes in our apartment had gotten so far under my skin over the weeks we'd been living there that I pretty much figured out immediately which chimes had stopped.
You guessed it — the girls' room. By the time I got in there they were both awake and holding hands while spinning like they teach you. My parents were in there a couple seconds after me, but only because they had farther to go.
Anyway, it was nothing much as vent problems go. A stuffed rabbit toy had gotten jammed into the fan — so the girls got grounded and had to do extra chores for a week. They whined about it, and kids do, and then we all went back to bed. It took a me good while to go back to sleep after that. For all I my complaining about those annoying, distracting, aggravating wind chimes, if we didn't have 'em up that night my sisters would have never have woken up.
Yeah, Fireproof is another absolute classic from grand-master Hal Clement. And it hammers home a hard truth you can find in Lazarus Long's notebooks. On Terra, being ignorant shortens your lifespan. Being willfully ignorant is just asking for it.
And being willfully ignorant in space means you are doing your darndest to cop a Darwin Award. You don't just need a good education to get a job in space, you need so you don't die. Read how that moron saboteur Hart thinks education is a waste of time.
Up to when his flaming body gets splattered all over the wall because he thinks he's so smart. He thinks Nah, I don't need no stinkin' physics and chemistry! That's the last thing that goes through his brain, besides the bulkhead. If Igno-Spy had ever had a high-school Science class he might have realized he was turning the inside of his jail cell into a freaking free-fall thermobaric weapon. With him flicking his Bic at the fuse like Wile E. To conserve his oxygen supply, the curly-haired cadet had set the controls of his boat on a steady orbit around one of the larger asteroids and lay down quietly on the deck.
One of the first lessons he had learned at Space Academy was, during an emergency in space when oxygen was low, to lie down and breath as slowly as possible.
And, if possible, to go to sleep. Sleep, under such conditions, served two purposes. While relaxed in sleep, the body used less oxygen and should help fail to arrive, the victim would slip into a suffocating unconsciousness, not knowing if and when death took the place of life.
Unpleasant odors in the air is a problem, but there is not much one can do about it. After all, you can't just open up a window to let in some fresh air, not in the vacuum of space. NASA carefully screens all materials, sealants, foods, and everything else to ensure that they do not emit noticeable odor in the pressurized habitat sections of spacecraft and space stations.
Such odors can quickly become overpowering in such tight quarters. There's a fortune awaiting the man who invents a really good deodorizer for a spaceship. That's the one thing you can't fail to notice. Oh, they try, I grant them that. The air goes through precipitators each time it is cycled; it is washed, it is perfumed, a precise fraction of ozone is added, and the new oxygen that is put in after the carbon dioxide is distilled out is as pure as a baby's mind; it has to be, for it is newly released as a by-product of the photosynthesis of living plants.
That air is so pure that it really ought to be voted a medal by the Society for the Suppression of Evil Thoughts. Besides that, a simply amazing amount of the crew's time is put into cleaning, polishing, washing, sterilizing - oh, they try! But nevertheless, even a new, extra-fare luxury liner like the Tricorn simply reeks of human sweat and ancient sin, with undefinable overtones of organic decay and unfortunate accidents and matters best forgotten.
Once I was with Daddy when a Martian tomb was being unsealed - and I found out why xenoarchaeologists always have gas masks handy. But a spaceship smells even worse than that tomb. It does no good to complain to the purser. He'll listen with professional sympathy and send a crewman around to spray your stateroom with something which I suspect merely deadens your nose for a while.
But his sympathy is not real, because the poor man simply cannot smell anything wrong himself. He has lived in ships for years; it is literally impossible for him to smell the unmistakable reek of a ship that has been lived in - and, besides, he knows that the air is pure; the ship's instruments show it.
None of the professional spacers can smell it. But the purser and all of them are quite used to having passengers complain about the "unbearable stench" - so they pretend sympathy and go through the motions of correcting the matter. Not that I complained. I was looking forward to having this ship eating out of my hand, and you don't accomplish that sort of coup by becoming known first thing as a complainer. But other first-timers did, and I certainly understood why - in fact I began to have a glimmer of a doubt about my ambitions to become skipper of an explorer ship.
But - Well, in about two days it seemed to me that they had managed to clean up the ship quite a bit, and shortly thereafter I stopped thinking about it.
I began to understand why the ship's crew can't smell the things the passengers complain about. Their nervous systems simply cancel out the old familiar stinks - like a cybernetic skywatch canceling out and ignoring any object whose predicted orbit has previously been programmed into the machine.
But the odor is still there. I suspect that it sinks right into polished metal and can never be removed, short of scrapping the ship and melting it down. Thank goodness the human nervous system is endlessly adaptable. His hole was on the eighth level, off a residential tunnel a hundred meters wide with fifty meters of carefully cultivated green park running down the center.
The main corridor's vaulted ceiling was lit by recessed lights and painted a blue that Havelock assured him matched the Earth's summer sky. Living on the surface of a planet, mass sucking at every bone and muscle, and nothing but gravity to keep your air close, seemed like a fast path to crazy. The blue was nice, though. Some people followed Captain Shaddid's lead by perfuming their air.
Not always with coffee and cinnamon scents, of course. Havelock's hole smelled of baking bread. Others opted for floral scents or semipheromones. Candace, Miller's ex-wife, had preferred something called EarthLily, which had always made him think of the waste recycling levels.
These days, he left it at the vaguely astringent smell of the station itself. Recycled air that had passed through a million lungs. The circle of life on Ceres was so small you could see the curve. He liked it that way. Infinitely more serious than annoying odors are harmful atmospheric contaminants.
They share the same problem that a spacecraft cannot open the windows to bring in some fresh air. But unlike odors, these can harm or kill. Basic atmospheric monitors will keep an eye on the breathing mix inside the habitat module for oxygen and carbon dioxide levels.
But prudent spacecraft will have monitors for carbon monoxide and other deadly gases, hooked up to strident alarms. In space no one can hear you scream, but in the habitat module's atmosphere everybody can hear that high-pitched squeaky wheel in the ventilator.
And there may be permanent hearing loss from loud noises, say, from rocket engines. As a point of reference, the normal ambient noise level on the International Space Station is 60 db. Acoustic criteria are specified in terms of A-weighted sound level L A or equivalent A-weighted sound level L eq , where it is a specified time period, usually 8 or 24 hours.
The equivalent A-weighted sound level is defined as the constant sound level that, in a given situation and time period, conveys the same sound energy as the actual time varying A-weighted sound.
The basic unit for these measurements is the decibel. Space station laboratory modules should have A-weighted sound levels not exceeding 55 dB a noise criterion curve of approximately 50 and reverberation times not exceeding 1. These values should permit 95 percent intelligibility for sentences under conditions of normal vocal effort with the talker and the listener visible to each other.
Environments with A-weighted sound levels above 55 dB will require assistance for adequate speech communication. Designers of audiecommunication systems should recognize that the systems will amplify and distribute noise as well as speech signals to both intended and unintended listeners.
Therefore, their use should be carefully controlled. For sleeping areas, background A-weighted sound levels below 45 dB are preferred, while levels up to 60 dB A are acceptable. Brief noises or transients during continuous noise backgrounds are particularly disturbing to sleep.
The probability of full behavioral awakening increases with increasing sound level of the transient. For transients with an L A of 60 dB, the probability of full behavioral awakening is about 0. The risk for producing significant hearing loss is negligible in noise exposures to an L eq24 of 80 dB.
A hearing conservation program similar to that described by the Occupational Safety and Health Administration should be initiated for exposures to an L eq8 of 85 dB or more. If acoustic requirements for acceptable speech communication, sleep, and hearing conservation are met, problems of annoyance and task disruption will be minimal. Vibration criteria are specified for linear vibration in the Hz frequency range. To reduce the probability of motion sickness, it is recommended that acceleration not exceed 2.
Specific tasks requiring more stringent vibrational criteria should be analyzed on an individual basis. In the absence of appropriate information, these tasks should be simulated on earth to determine vibration sensitivity and required accuracy.
If head or finger control is required to an accuracy of 5mm rms or 2. Hypergolics hiss too, with a harsher metallic note, bangs and pings. Hydroxy rockets , they roar. Solid packs are similar, but rougher, with underlying stutters and clicks. You hear it with your bones. Hard burn, in the jargon, refers to the practice of injecting a limited supply of antiprotons into the exhaust of a fusion torch for short, high-power bursts.
Former astronaut Jay Buckey, now at Dartmouth Medical School in Hanover, New Hampshire, US, says that both temporary and permanent hearing loss were recorded after flights on the Soviet and Russian Salyut and Mir stations, even for stays as short as seven days. The lost hearing was usually at higher frequencies.
The living quarters of the ISS are the Russian Zvezda module, which is the noisiest module on the station. NASA says the goal is for the working area to have noise levels at or below 60 decibels dB and sleep bunks to be 50dB. At their peak several years ago, noise levels reached 72 to 78dB in the working area and 65 dB in the sleep stations. Decibels are measured on a logarithmic scale, meaning, for example, that 60dB is 10 times louder than 50dB.
NASA has worked to reduce the noise and its effect on the crew. By November , noise levels had been lowered to between 62 to 69dB in the work area and 55 to 60dB in the sleep compartments. Astronauts on the ISS used to have to wear ear plugs all day but are now only wear them for 2 to 3 hours per work day.
According to the US National Institutes of Health, however, noise levels below 80dB are unlikely to lead to hearing loss, even with prolonged exposure. But while the primary cause of hearing loss in general is high noise levels, Buckey suggested in a paper in Aviation Space and Environmental Medicine that several other factors might contribute to the problem in space.
Elevated intracranial pressure, higher carbon dioxide levels and atmospheric contaminants may make the inner ear more sensitive to noise, he says. Water is the key to ensuring that the kidneys function as they should and wastes are flushed from the body. Cartilage in the body — the cushioning agent of joints and discs of the spine — consists of about 80 percent water. So when cartilage becomes dried out, it follows that the joints are less able to shrug off bumps and knocks.
Instead, they can feel stiff or bristle with pain. Just as your appetite for food fluctuates, so does your thirst for water, and staying tuned to your body's signal for water is the best way to ensure you drink enough, especially since the amount of water you lose every day pivots on how much you perspire and excrete through urine and bowel movements. These recommendations can seem high, but remember that some of the water we get comes from our food. For example, certain vegetables like zucchini and fruit like watermelon teem with water, which can help you meet your recommended daily intake.
When you find yourself craving sugary drinks, remember the empty calories they contain. Water may be bland, but its attributes can't be denied.
As the Mayo Clinic says: If you can't see the world, then you may as well try to meet or at least talk to everyone in it. So goes the hopeful thinking of many journalists, including Mary Wroblewski.
This is why you'll see her work in a wide variety of publications, especially those in the business, education, health care and nutrition genres. Mary came of age as a reporter and editor in some of Chicago's scrappiest newsrooms but softened up long enough to write nine children's books as well as one nonfiction tome.
Skip to main content. Healthy Eating Nutrition Nutrition in Foods. Wroblewski; Updated May 12, Water is essential to proper functioning of your body. Water Is Your Body's Fuel About 60 percent of your body consists of water, which may sound like a lot until you realize how far that water must travel and the functions it must perform — every single day.
Cardiovascular system — heart and blood vessels. Most platyhelminths have no anus and regurgitate undigested material through the mouth. However, some long species have an anus and some with complex, branched guts have more than one anus, since excretion only through the mouth would be difficult for them. Some species break up and soften food first by secreting enzymes in the gut or pharynx throat. All animals need to keep the concentration of dissolved substances in their body fluids at a fairly constant level.
Internal parasites and free-living marine animals live in environments with high concentrations of dissolved material, and generally let their tissues have the same level of concentration as the environment, while freshwater animals need to prevent their body fluids from becoming too dilute.
Despite this difference in environments, most platyhelminths use the same system to control the concentration of their body fluids.
Flame cells , so called because the beating of their flagella looks like a flickering candle flame, extract from the mesenchyme water that contains wastes and some reusable material, and drive it into networks of tube cells which are lined with flagella and microvilli. The tube cells' flagella drive the water towards exits called nephridiopores , while their microvilli reabsorb reusable materials and as much water as is needed to keep the body fluids at the right concentration.
These combinations of flame cells and tube cells are called protonephridia. In all platyhelminths, the nervous system is concentrated at the head end. This is least marked in the acoels , which have nerve nets rather like those of cnidarians and ctenophores , but densest around the head.
Other platyhelminths have rings of ganglia in the head and main nerve trunks running along their bodies. Early classification divided the flatworms in four groups: Turbellaria, Trematoda, Monogenea and Cestoda.
This classification had long been recognized to be artificial, and in , Ehlers  proposed a phylogenetically more correct classification, where the massively polyphyletic "Turbellaria" was split into a dozen orders, and Trematoda, Monogenea and Cestoda were joined in the new order Neodermata.
However, the classification presented here is the early, traditional, classification, as it still is the one used everywhere except in scientific articles. Most are predators or scavengers, and terrestrial species are mostly nocturnal and live in shaded, humid locations, such as leaf litter or rotting wood.
However, some are symbiotes of other animals, such as crustaceans , and some are parasites. Free-living turbellarians are mostly black, brown or gray, but some larger ones are brightly colored.
Some turbellarians have a simple pharynx lined with cilia and generally feed by using cilia to sweep food particles and small prey into their mouths, which are usually in the middle of their undersides. Most other turbellarians have a pharynx that is eversible can be extended by being turned inside-out , and the mouths of different species can be anywhere along the underside. Most turbellarians have pigment-cup ocelli "little eyes" ; one pair in most species, but two or even three pairs in others.
A few large species have many eyes in clusters over the brain, mounted on tentacles, or spaced uniformly around the edge of the body. The ocelli can only distinguish the direction from which light is coming to enable the animals to avoid it. A few groups have statocysts - fluid-filled chambers containing a small, solid particle or, in a few groups, two. These statocysts are thought to function as balance and acceleration sensors, as they perform the same way in cnidarian medusae and in ctenophores.
However, turbellarian statocysts have no sensory cilia, so the way they sense the movements and positions of solid particles is unknown. On the other hand, most have ciliated touch-sensor cells scattered over their bodies, especially on tentacles and around the edges.
Specialized cells in pits or grooves on the head are most likely smell sensors. Planarians , a subgroup of seriates, are famous for their ability to regenerate if divided by cuts across their bodies. Experiments show that in fragments that do not already have a head a new head grows most quickly on those fragments which were originally located closest to the original head. This suggests the growth of a head is controlled by a chemical whose concentration diminishes throughout the organism, from head to tail.
Many turbellarians clone themselves by transverse or longitudinal division, whilst others, especially acoels, reproduce by budding.
The vast majority of turbellarians are hermaphrodites they have both female and male reproductive cells which fertilize eggs internally by copulation. Trematodes are divided into two groups, Digenea and Aspidogastrea also known as Aspodibothrea. These are often called flukes, as most have flat rhomboid shapes like that of a flounder Old English flóc. There are about 11, species, more than all other platyhelminthes combined, and second only to roundworms among parasites on metazoans.
The intermediate stages transfer the parasites from one host to another. The definitive host in which adults develop is a land vertebrate; the earliest host of juvenile stages is usually a snail that may live on land or in water, whilst in many cases a fish or arthropod is the second host. Schistosomes, which cause the devastating tropical disease bilharzia , belong to this group. Adults range between 0.
Individual adult digeneans are of a single sex, and in some species slender females live in enclosed grooves that run along the bodies of the males, partially emerging to lay eggs. In all species the adults have complex reproductive systems, capable of producing between 10, and , times as many eggs as a free-living flatworm.
In addition, the intermediate stages that live in snails reproduce asexually. Adults of different species infest different parts of the definitive host - for example the intestine , lungs , large blood vessels,  and liver. In both the adult and snail-inhabiting stages, the external syncytium absorbs dissolved nutrients from the host. Adult digeneans can live without oxygen for long periods. Members of this small group have either a single divided sucker or a row of suckers that cover the underside.
These parasites attach themselves to their hosts by means of disks that bear crescent-shaped hooks. They are divided into the Monogenea and Cestoda groupings. Of about 1, species of monogeneans, most are external parasites that require particular host species - mainly fish, but in some cases amphibians or aquatic reptiles.
However, a few are internal parasites. They often have flattened bodies. In some species, the pharynx secretes enzymes to digest the host's skin, allowing the parasite to feed on blood and cellular debris. Others graze externally on mucus and flakes of the hosts' skins. The name "Monogenea" is based on the fact that these parasites have only one nonlarval generation.
These are often called tapeworms because of their flat, slender but very long bodies — the name "cestode" is derived from the Latin word cestus , which means "tape". The adults of all 3, cestode species are internal parasites.